The John H. Stroger, Jr. Hospital of Cook County, formerly Cook County Hospital is a public urban teaching hospital in Chicago that provides primary, specialty and tertiary healthcare services to the five million residents of Cook County, Illinois. The hospital has a staff of 300 attending physicians along with more than 400 medical residents and fellows. The hospital campus, located at 1901 W. Harrison Street Chicago, Illinois, is a part of the 305-acre (123 ha) Illinois Medical District, which is one of the largest concentrations of medical facilities in the world.